1. Field of the Invention
The present invention relates to an accelerating grid, particularly for an ion beam, consisting of at least one orifice plate which is fastened along the outer rim thereof to a support, and which includes a plurality of through-holes with mutually oriented central axes, preferably directed towards a common focusing point.
2. Discussion of the Prior Art
Known accelerating grids of this type, such as should generally find utilization as ion beam grids in the nuclear fusion technology, and which then mostly consist of a plurality of cooled sequentially arranged orifice plates with axial alignment of their through-holes, at which there are applied different high-voltage potentials to each grid so that the ions during passing through of the grid will be concurrently highly accelerated and focused, are combined of planar orifice plates or plate segments which are rigidly clamped on a support, and during operation are subjected to a considerable thermal load and heat expansion, under the effect of which this will lead to a wide deviation of the central axes of their through-holes from the nominal focusing point and among the individual orifice plates to such extensive relative displacements, that there is exceeded the permissable tolerance range in the plate spacing and there is produced an extensive localized offset of the central axes between the through-holes of neighboring orifice plates. This produces the consequence that the ion-optical properties of the accelerating grid will be markedly disturbed.